Broken tool detector

ABSTRACT

A portion of a pneumatic circuit for sensing the breakage of a punch is formed by a normally closed passageway in the punch itself. If the punch is broken, the passageway is opened up and pressurized air in the circuit is vented to the atmosphere through the passageway. A pressure differential switch in the circuit senses the resulting pressure change and, in response thereto, produces an electric signal to indicate breakage of the tool.

United States Patet 91 Scott [451 Apr. 24, 1973 BROKEN TOOL DETECTOR2,953,044 9/1960 Kimble etal. ..408/6 Inventor: William B. ScottSteward, m- 3,24l,402 3/1966 Crowell et a1. ..408/6 [73] Assignee: W. A.Whitney C0rp., Rockford, lll. Primary Examiner--Andrew R. .luhaszAtt0rneyW0lfe, Hubbard, Leydig, Voit & Osann, [22] Filed. Nov. 15, 1971Ltd [21] Appl. No.: 198,689

[57] ABSTRACT 52 US. Cl. ..83/62, 83/686, 175/39, A Portion of aPneumatic circuit for sensing the 408/6 breakage of a punch is formed bya normally closed 51 1 Int. CL 2 7/22 E2 lb 13/00 1323 49/00 passagewayin the punch itself. If the punch iS broken, [58] Field of Search..83/62 686' 408/6- the passageway is p ned up and pressurized air inthe circuit is vented to the atmosphere through the passageway. Apressure differential switch in the cir- References Cited cuit sensesthe resulting pressure change and, in

response thereto, produces an electric signal to in- UNITED STATESPATENTS dicate breakage of the tool.

2,468,905 5/l949 Warren, Jr. ..l75/39 5 Claims, 3 Drawing Figures BROKENTOOL DETECTOR BACKGROUND OF THE INVENTION The present invention relatesto a detector for use in a machine tool to sense the breakage of a toolelement and, more particularly, to a detector of the type in whichbreakage of the tool element is sensed by detecting pressure changeswhich occur in a pneumatic circuit as a result of the tool breaking.

SUMMARY OF THE INVENTION The general object of the present invention isto provide a new and improved broken tool detector of the above generalcharacter which is simpler, less expensive and easier to use than priordetectors.

A further object is to provide a detector which is particularly adaptedfor use with reciprocating tools and which is quicker to signal that thetool element has been broken so that damage to the workpiece or themachine tool can be avoided.

Another important object is to provide a detector including, in additionto the foregoing advantages, a pressure circuit which is hooked up andready for operation as an incident to normal installation of the toolelement and which does not inhibit the tool changing operation orintroduce additional time consuming steps in order to put the detectorinto service.

In a more detailed sense, the invention resides in the unique and simpleconstruction of an air passage in the tool element itself, the passageforming part of and normally closing the pneumatic circuit but openingup and venting the circuit to atmosphere upon breakage of the toolthereby to create a pressure change indicative of the breakage.

These and other objects and advantages of the present invention willbecome readily apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of thebroken tool detector system embodying the novel features of the presentinvention.

FIG. 2 is an enlarged elevational view of an exemplary tool adapted foruse in the system.

FIG. 3 is an enlarged elevational view of a broken tool.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in thedrawings for purposes of illustration, the present invention is embodiedin a machine tool with a movable carrier 11 which supports atool element13 for performing work on a workpiece l4. Herein, the machine toolincludes a novel system for detecting the breakage of the tool elementduring the normal operation of the machine tool.

While the detector system of the present invention is equally wellsuited for use in many various types of machine tools, the machine tool10 disclosed specifically herein is a punch press and the carrier 11 isa reciprocable ram. The tool element 13 is a punch which is supported onthe lower end of the ram by a punch holder 15. In operation, the ram isreciprocated in response to the admission of hydraulic oil alternatelyinto opposite ends ofa cylinder 16 housing a piston 16a to which the ramis connected. On the downstroke of the ram, the punch is driven throughthe workpiece 14 and into an underlying die 14a to punch a hole in theworkpiece.

As shown in FIG. 1, the detector system includes a pneumatic circuit 17having a fluid pressure line 19 communicating with a pressure source 20and leading toward the punch 13. The downstream end of the line isblocked by the punch to keep air in the line from escaping. A pressureregulator 23 connected in the line keeps the air pressure in the line ata preselected value during normal punching operations. If the punch isbroken during a punching cycle, the end of the line is unblocked and aircan escape thus causing a change in the pressure in the line. To detectthis change from the preselected pressure value, a pressure detector 24is connected between the end of the line and the pressure regulator. Inresponse to detecting a change of pressure, the detector produces anelectric signal thereby indicating breakage of the punch.

Herein, the pressure detector 24 preferably includes an adjustablerestriction in the form of a needle valve 25 located in the fluidpressure line 19 to restrict the flow of air in the line past thedetector. As long as the punch 13 blocks the flow of air from the line,there is no or substantially no flow of air across the needle valve andas a result, there is practically no pressure drop across the needlevalve. When the punch 13 is broken, however, the air escapes rapidlyfrom that portion of the line downstream of the needle valve and causesa much faster flow of air through the needle valve from the upstreamportion of the line. This results in the creation of a larger pressuredrop across the opposite sides of the needle valve. A differentialpressure switch 26 is connected in parallel with the needle valve and issensitive to the differential pressure across the valve. When thedifferential pressure rises to a preselected level, the switch triggersand produces an electric signal indicative of breakage of the punch.

The signal may be used simply to turn on a light indicating to the punchpress operator that the punch 13 is broken or preferably, as in thepresent instance, the signal is used to shut down the automatic punchingcycle of the punch press 10 by de-energizing a relay 26a to causecentering of a valve (not shown) and thereby stop the flow of hydraulicoil to cylinder 16. In any event, it is desirable that the breakage ofthe punch be detected as soon as possible so that the punch press may bestopped quickly to keep the broken punch from causing damage to theworkpiece 14 or to the punch press itself. For this reason, the needlevalve 25 and pressure differential switch 26 arrangement is preferredover a simple pressure switch because of the quick response time of suchan arrangement.

In accordance with the primary aspect of the present invention,provision is made of a unique detector system whereby breakage of thepunch 13 is detected immediately and without the tool first having to beretracted away from the workpiece 14. For these purposes, the terminalportion of the pneumatic circuit 17 is formed within the punch itself sothat, when the punch breaks, the air in the. circuit is immediatelyvented to the atmosphere. More specifically, a normally closedpassageway 27 is formed in the punch and,

when the latter is mounted in the punch holder 15, the passagewaybecomes a part of the pneumatic circuit so that breakage of the punchwill open up and expose the passageway to allow the air in the circuitto escape and trigger the switch 26. With this unique arrangement,breakage of the tool element is detected immediately during the punchingcycle even if the punch is still in the workpiece 14. As a result,reciprocation of the ram 11 may be stopped to prevent damage whichotherwise might be caused by the broken tool,

In the present instance, the passageway 27 is a small cylindrical holedrilled axially through the punch 13 with the upper end 29 of the holeopening out the top surface 30 of the enlarged head 31 of the punch. Thelower end or bottom 33 of the hole terminates just short of the lowerend surface 34 of the punch and thus is closed off. Advantageously, whenthe punch is inserted into the holder 15, the upper end of thepassageway automatically aligns with a passage 32 formed axially throughthe ram and the holder and communicating with the pressure line 19.Thus, it will be appreciated that the pneumatic circuit 17 is completedand substantially closed off when the punch 13 is mounted on the end ofthe ram, the punch itself actually forming a portion of and closing offthe circuit by virtue of the open end 29 of the passageway 27communicating with the lower end of the passage 32 and by virtue of thelower end 33 of the passageway 27 being closed. Because the upper end ofthe passageway 27 may not form. a perfect seal with the lower end of thepassage 32, a small amount of air may be vented constantly between thepunch 13 and ram 11. This possible air leakage, however, would be sosmall as to cause no pressure drop across the needle valve 25.

When the punch 13 is broken, such as is shown in FIG. 3, the lower end33 of the passageway 27 is opened thereby permitting the pressurized airto escape from the circuit 17. This, in turn, triggers the pressuredifferential switch 26 to produce the signal indicating the breakage ofthe punch so that the punch press 10 may be shut down to enablereplacement of the broken punch. If the ram 11 is stopped automaticallyin its lowered position, the punch press operator can manually jog theram upwardly to a upper tool change position for the purpose ofreplacing the punch. Ad-

vantageously, when changing punches, the present detector system doesnot interfere with or complicate the tool changing process since thepunch 13 forms a part of the circuit 17 simply by being inserted intothe holder 15.

To further facilitate the changing of punches and to avoid unnecessarytriggering of the switch 26, a shut off valve 36 is located in the fluidpressure line 19 just downstream of the switch. The valve may be turnedoff to block the flow of air to the end of the pressure line whenchanging punches or when it is not desired to use the detector system.

lclaimas my invention:

1. in a machine tool for performing work on a workpiece, the combinationof, a tool carrier reciprocable toward and away from the workpiece, atool having a first end mountable on the carrier for movement therewithand having a second end for performing work on the workpiece when saidcarrier is reciprocated, a

passageway formed in said tool and terminating a dacen the second end ofthe tool, means for pressurizing said passageway with air to apreselected pressure, and means responsive to changes in said pressureresulting from breakage of the tool and venting of the terminal end ofthe passageway to produce a signal indicating the breakage.

2. A punch press having a ram reciprocable upwardly and downwardlyrelative to an underlying workpiece,'a punch carried on the lower end ofthe ram for punching a hole in said workpiece during the downstroke ofthe ram, the improvement in said press comprising, a pneumatic circuithaving a passage extending axially of said ram and opening out of thelower end thereof, a passageway extending from the upper end of saidpunch toward the lower end portion thereof and terminating within thepunch in said lower end portion, the upper end of said passagewaycommunicating with the lower end of said passage, means for introducingpressurized air into said passage to pressurize said passageway to apreselected pressure, and means for producing a signal in response tochanges in said pressure resulting from breakage of the punch andventing of the lower end of said passageway.

3. A punch press as defined by claim 2 wherein said signal producingmeans includes a pressure sensitive switch responsive to the pressurebetween said passageway and said pressurization means and operable toproduce an electrical signal as an incident to such pressure droppingbelow a preselected level.

4. A punch press as defined by claim 3 wherein said circuit includes anadjustable restriction located between and communicating with saidpressurization means and said passage, said pressure sensitive switchbeing a pressure differential switch located between and communicatingwith said pressurization means and said passage and connected inparallel across said restriction so as to be responsive to changes inthe differential pressure on opposite sides of the restriction.

5. A punch press having a ram reciprocable upwardly and downwardly insuccessive automatic cycles relative to an underlying workpiece, a punchcarried on the lower end of the ram for punching a hole in the workpieceduring the downstroke of the ram, said punch having an elongated bodywith an upper head and a lower punching surface, the improvement in saidpress comprising, a pneumatic circuit having a passage extending axiallythrough said ram and opening out the lower end thereof, a small holedrilled through the head of said punch, extending axially within saidbody and having a closed lower end spaced just upwardly from the lowerpunching surface of the punch, said hole communicating with said passageforming a portion of said circuit so that the circuit will be vented tothe atmosphere when the lower end portion of the punch is broken to openup the lower end of said hole, means for normally pressurizing thecircuit to a preselected pressure different than atmospheric pressure sothat the pressure in the circuit will change when the circuit is ventedto the atmosphere upon breaking of said punch, and means operable inresponse to such change in the pressure of the circuit to terminateautomatic cycling of the ram.

1. In a machine tool for performing work on a workpiece, the combinationof, a tool carrier reciprocable toward and away from the workpiece, atool having a first end mountable on the carrier for movement therewithand having a second end for performing work on the workpiece when saidcarrier is reciprocated, a passageway formed in said tool andterminating adjacent the second end of the tool, means for pressurizingsaid passageway with air to a preselected pressure, and means responsiveto changes in said pressure resulting from breakage of the tool andventing of the terminal end of the passageway to produce a signalindicating the breakage.
 2. A punch press having a ram reciprocableupwardly and downwardly relative to an underlying workpiece, a punchcarried on the lower end of the ram for punching a hole in saidworkpiece during the downstroke of the ram, the improvement in saidpress comprising, a pneumatic circuit having a passage extending axiallyof said ram and opening out of the lower end thereof, a passagewayextending from the upper end of said punch toward the lower end portionthereof and terminating within the punch in said lower end portion, theupper end of said passageway communicating with the lower end of saidpassage, means for introducing pressurized air into said passage topressurize said passageway to a preselected pressure, and means forproducing a signal in response to changes in said pressure resultingfrom breakage of the punch and venting of the lower end of saidpassageway.
 3. A punch press as defined by claim 2 wherein said signalproducing means includes a pressure sensitive switch responsive to thepressure between said passageway and said pressurization means andoperable to produce an electrical signal as an incident to such pressuredropping below a preselected level.
 4. A punch press as defined by claim3 wherein said circuit includes an adjustable restriction locatedbetween and communicating with said pressurization means and saidpassage, said pressure sensitive switch being a pressure differentialswitch located between and communicating with said pressurization meansand said passage and connected in parallel across said restriction so asto be responsive to changes in the differential pressure on oppositesides of the restriction.
 5. A punch press having a ram reciprocableupwardly and downwardly in successive automatic cycles relative to anunderlying workpiece, a punch carried on the lower end of the ram forpunching a hole in the workpiece during the downstroke of the ram, saidpunch having an elongated body with an upper head and a lower punchingsurface, the improvement in said press comprising, a pneumatic circuithaving a passage extending axially through said ram and opening out thelower end thereof, a small hole drilled through the head of said punch,extending axially within said body and having a closed lower end spacedjust upwardly from the lower punching surface of the punch, said holecommunicating with said passage forming a portion of said circuit sothat the circuit will be vented to the atmosphere when the lower endportion of the punch is broken to open up the lower end of said hole,means for normally pressurizing the circuit to a preselected pressuredifferent than atmospheric pressure so that the pressure in the circuitwill change when the circuit is vented to the atmosphere upon breakingof said punch, and means operable in response to such change in thepressure of the circuit to terminate automatic cycling of the ram.